Various types of magnetic field sensing elements are known, including Hall Effect elements and magnetoresistance elements. Magnetic field sensors generally include a magnetic field sensing element and other electronic components. Some magnetic field sensors also include a permanent magnet in a so-called “back biased” arrangement described more fully below.
Magnetic field sensors provide an electrical signal representative of a sensed magnetic field. In some embodiments that have the magnet in a so-called back-biased arrangement, a magnetic field sensed by a magnetic field sensor is a magnetic field generated by the magnet.
In these back-biased arrangements, in the presence of a moving ferromagnetic object, the magnetic field generated by the magnet and sensed by the magnetic field sensor varies in accordance with a shape or profile of the moving ferromagnetic object.
In some arrangements, the ferromagnetic object that is sensed can have teeth, as in gear teeth upon a gear. With these arrangements, passing gear teeth are sensed and by the magnetic field sensor, a rate of which can be indicative of a speed of rotation of the gear. An output signal from the magnetic field sensor can indicate the speed of the rotation.
With some arrangements, the output signal from the magnetic field sensor can also indicate a direction of the rotation.
Where the gear is attached to a target object, for example, a shaft, the output signal from the magnetic field sensor can be indicative of the speed of rotation of the target object and/or the direction of rotation of the target object.
Magnetic field sensing elements, e.g., Hall effect elements, can be used to sense the varying magnetic field in response to passing ferromagnetic object, e.g., a rotating gear. In some arrangements, a relative phase of signals generated by two or more of the magnetic field sensing elements is used to detect the direction of rotation of the ferromagnetic object, e.g., the gear. Thus, it will be apparent that a small relative phase difference, particularly in the presence of electrical or magnetic noise, can result in errors in the detection of the direction of rotation.
It would be desirable to provide a magnetic field sensor in a back-biased arrangement that can achieve an output signal that accurately differentiates between two directions of rotation of a ferromagnetic object to provide a detected direction, with reduced susceptibility to errors in the detected direction.